feat: add dedicated Security page and policy-pack foundation (#1362)

* feat: add dedicated Security page and policy-pack foundation

Bring vulnerability scanning, scan history, suppressions, Compose risks,
secrets, policy packs, and scanner setup into one node-scoped Security
command center instead of scattering them across Resources and Settings.

- New top-level Security view with Overview, Images, Compose risks,
  Secrets, Policies, Suppressions, History, and Scanner setup tabs
  (status masthead + signal rail; controlled tabs with deep-link support).
- Backend: GET /security/overview rollup and GET /security/policy-packs
  static catalog (auth-only, Community). DatabaseService gains an uncapped
  scan-status count and a node-eligible block-policy count, and
  getImageScanSummaries now projects secret and misconfig counts.
- Reuse existing surfaces: the scan-history sheet, the control-governed
  suppression and acknowledgement panels, and the scan-detail sheet (now
  with an initial-tab prop so it opens on the matching finding type).
- Extract a shared SeverityBadge (from Resources) and a TrivyManager
  (from Settings) so both surfaces render identical controls.
- Resources "Scan history" now links into the Security page History tab.
- Docs for the new Security surface and tests for the new endpoints,
  helpers, nav wiring, and tabs.

* refactor: consolidate scanner and policy management onto the Security page

Remove the Settings "Vulnerability Scanning" section now that the Security
page covers the same ground, with every option preserved:

- Scanner install / update / uninstall / auto-update live on the Scanner setup
  tab (TrivyManager).
- Scan policies, the honor-suppressions toggle, and the replica
  managed-by-control / demote controls move into a new ScanPolicyManager on the
  Policies tab (paid; Community sees only the policy-pack catalog).
- CVE suppressions and acknowledgements remain on the Suppressions tab.

Wiring removed: the registry section and the now-empty Security settings group,
the SectionId, the SettingsSectionContent case and the isPaid prop it was the
sole consumer of, and SecuritySection itself. The dashboard configuration-status
"Vulnerability scanning" row now navigates to the Security page Policies tab.

Docs that pointed at "Settings -> Security -> Vulnerability Scanning" are swept
to the relevant Security page tabs.

* fix: harden Security page scanner refresh, policy-load errors, and secret-only badges

Address independent-review findings on the Security page:

- Scanner setup now refreshes Trivy state when the active node changes, so the
  displayed scanner status matches the node TrivyManager's actions target (both
  follow x-node-id). Previously, switching nodes on the tab left stale state.
- ScanPolicyManager surfaces an explicit error state on a failed policy fetch
  instead of falling through to a false "No scan policies configured".
- The shared SeverityBadge and the Images findings column no longer label a scan
  "clean" when it has secrets or misconfigurations but no CVE severity
  (highest_severity is derived from vulnerabilities only); they show a "Findings"
  state and the secret/misconfig counts instead.
- The Overview enforcement note points to the Policies tab, not the removed
  Settings section.
- The History tab auto-opens the scan-history sheet only on a deep-link (mount
  with the History tab active), not on every manual tab selection.

Adds tests for the badge secret/misconfig state and the policy-load error state.

frontend/src/types/security.ts

@@ -136,6 +136,8 @@ export interface ScanSummary {
   low: number;
   unknown: number;
   fixable: number;
+  secret_count: number;
+  misconfig_count: number;
 }
 
 export interface ScanPolicy {
@@ -175,3 +177,50 @@ export interface ScanCompareResult {
   truncated?: boolean;
   row_limit?: number;
 }
+
+/** Node-scoped security posture rollup for the Security page Overview. */
+export interface SecurityOverview {
+  scannedImages: number;
+  critical: number;
+  high: number;
+  fixable: number;
+  secrets: number;
+  misconfigs: number;
+  staleScans: number;
+  failedScans: number;
+  lastSuccessfulScanAt: number | null;
+  scanner: {
+    available: boolean;
+    version: string | null;
+    source: TrivySource;
+    autoUpdate: boolean;
+  };
+  deployEnforcement: {
+    honorSuppressionsOnDeploy: boolean;
+    /** Approximate count of enabled block-on-deploy policies eligible for this node. */
+    eligibleBlockPolicies: number;
+  };
+}
+
+/** Which detail tab the scan sheet opens on. Matches VulnerabilityScanSheet's tabs. */
+export type ScanDetailTab = 'vulns' | 'secrets' | 'misconfigs';
+
+export type PolicyRuleEnforcement = 'warning' | 'enforceable';
+
+export interface PolicyPackRule {
+  id: string;
+  name: string;
+  severity: Exclude<VulnSeverity, 'UNKNOWN'>;
+  whatItChecks: string;
+  why: string;
+  howToFix: string;
+  enforcement: PolicyRuleEnforcement;
+}
+
+export interface PolicyPack {
+  id: string;
+  name: string;
+  tagline: string;
+  tierCopy: string;
+  rules: PolicyPackRule[];
+}